011-ThreadFactory线程工厂

一、源码分析

　　ThreadFactory是一个线程工厂。用来创建线程。这里为什么要使用线程工厂呢？其实就是为了统一在创建线程时设置一些参数，如是否守护线程。线程一些特性等，如优先级。通过这个TreadFactory创建出来的线程能保证有相同的特性。它首先是一个接口类，而且方法只有一个。就是创建一个线程。

public interface ThreadFactory {
    Thread newThread(Runnable r);
}  

1》ThreadPoolExecutor创建

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }

最终均会调用创建以下构造方法

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

2》查看 Executors.defaultThreadFactory()实现

    public static ThreadFactory defaultThreadFactory() {
        return new DefaultThreadFactory();
    }

　　在JDK中，有实现ThreadFactory就只有一个地方。而更多的时候，我们都是继承它然后自己来写这个线程工厂的。

　　下面的代码中在类Executors当中。默认的 我们创建线程池时使用的就是这个线程工厂

static class DefaultThreadFactory implements ThreadFactory {
    private static final AtomicInteger poolNumber = new AtomicInteger(1);//原子类，线程池编号
    private final ThreadGroup group;//线程组
    private final AtomicInteger threadNumber = new AtomicInteger(1);//线程数目
    private final String namePrefix;//为每个创建的线程添加的前缀  

    DefaultThreadFactory() {
        SecurityManager s = System.getSecurityManager();
        group = (s != null) ? s.getThreadGroup() :
                              Thread.currentThread().getThreadGroup();//取得线程组
        namePrefix = "pool-" +
                      poolNumber.getAndIncrement() +
                     "-thread-";
    }  

    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r,
                              namePrefix + threadNumber.getAndIncrement(),
                              0);//真正创建线程的地方，设置了线程的线程组及线程名
        if (t.isDaemon())
            t.setDaemon(false);
        if (t.getPriority() != Thread.NORM_PRIORITY)//默认是正常优先级
            t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
} 

　　在上面的代码中，可以看到线程池中默认的线程工厂实现是很简单的，它做的事就是统一给线程池中的线程设置线程group、统一的线程前缀名。以及统一的优先级。

2、以下是自己实现ThreadFactory示例

package com.func.axc.threadfactory;

import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ThreadFactory;

/**
 */
public class ThreadFactoryTest {

    static class MyThreadFactory implements ThreadFactory {

        private int counter;
        private String name;
        private List<String> stats;

        public MyThreadFactory(String name) {
            counter = 0;
            this.name = name;
            stats = new ArrayList<String>();
        }

        @Override
        public Thread newThread(Runnable run) {
            Thread t = new Thread(run, name + "-Thread-" + counter);
            counter++;
            stats.add(String.format("Created thread %d with name %s on%s\n",t.getId(), t.getName(), new Date()));
            return t;
        }

        public String getStas() {
            StringBuffer buffer = new StringBuffer();
            Iterator<String> it = stats.iterator();
            while (it.hasNext()) {
                buffer.append(it.next());
                buffer.append("\n");
            }
            return buffer.toString();
        }

    }

    static class MyTask implements Runnable {

        private int num;

        public MyTask(int num) {
            this.num = num;
        }

        @Override
        public void run() {
            System.out.println("Task "+ num+" is running");
            try {
                Thread.sleep(2*10000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

    }

    public static void main(String[] args) {
        System.out.println("main thread beging");
        MyThreadFactory factory = new MyThreadFactory("MyThreadFactory");  

        Thread thread = null;
        for(int i = 0; i < 10; i++) {
            thread = factory.newThread(new MyTask(i));
            thread.start();
        }
        System.out.printf("Factory stats:\n");
        System.out.printf("%s\n",factory.getStas());
        System.out.println("main thread end");
    }

}